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HTML5Using Games to Learn HTML5 and JavaScript
CONTENTSThe Essential Guide to       HTML5  Using Games to Learn HTML5 and JavaScript             Jeanine Meyer           ...
CONTENTS      The Essential Guide to HTML5: Using      Games to Learn HTML5 and JavaScript                                ...
CONTENTSTo Daniel, Aviva, Anne, Esther, and Joseph, who is still in our lives, and for the newest members of              ...
CONTENTS     Contents at a Glance     Contents at a Glance...................................................................
CONTENTSContentsContents at a Glance.........................................................................................
CONTENTS       Testing and uploading the application.........................................................................
CONTENTS     Drawing text ...................................................................................................
CONTENTS       Building the application and making it your own ..............................................................
CONTENTS  Testing and uploading the application..............................................................................
CONTENTS    About the Author                            Jeanine Meyer is a Full Professor at Purchase College/State Univer...
CONTENTSAbout the Technical ReviewerCheridan Kerr has been involved in Web Development and Design since 1997 when she bega...
CONTENTS  Acknowledgments  Much appreciation to my students and colleagues at Purchase College/State University of New Yor...
CONTENTSIntroductionThere s been considerable enthusiasm about the new capabilities of HTML5, and even suggestions thatno ...
INTRODUCTION  CONTENTS  JavaScript, or general programming methodology that satisfy the requirements. Finally, we examine ...
Chapter 1 The Basics In this chapter, we will cover        •    the basic structure of an HTML document        •    the ht...
CHAPTER 1    The latest version of HTML (and its associated CSS and JavaScript) is HTML5. It is generating    considerable...
THE BASICS Figure 1-2. Favorite sites, with extra formatting When you reload the Favorite Sites page, the date and time wi...
CHAPTER 1HTML5, CSS, and JavaScript features    As I noted, HTML documents are text, so how do we specify links, pictures,...
THE BASICSIn most cases, you will create something within the body of the web page that you ll think of as a title, but it...
CHAPTER 1    <a href="http://faculty.purchase.edu/jeanine">    <img src="jhome.gif" width="100" />    </a>    Let s put th...
THE BASICS<head><title>Second example </title><body>This will appear as is. <br/><img src="frog.jpg"/><br/><img src="frog....
CHAPTER 1    this lets you easily change the formatting and the interactions. Formatting, including document layout, is a ...
THE BASICS          color: #EE015;          text-align:center;          font-size:22px;}section {        width:85%;       ...
CHAPTER 1 Figure 1-6. Sample CSS styles Tip: Don t be concerned if you don t understand everything immediately—you ll find...
THE BASICS statements, and statements that create what are called programmer-defined functions. A function is one or more ...
CHAPTER 1 processing program, which may insert non-text characters. Notepad also works, though TextPad has benefits such a...
THE BASICSNotice that I gave the file a name and that I can also change the folder from My Documents to somethingelse if I...
CHAPTER 1 Table 1-1. The “My games” Annotated Links Code Code                                                 Explanation ...
THE BASICSCode                                              ExplanationThe <a href="slingshot.html">Slingshot</a>        S...
CHAPTER 1 Code                                                          Explanation The <a href="maze.html">Maze</a> progr...
THE BASICSCode                                  Explanation    border:2px green double;          The border is a 2-pIxel g...
CHAPTER 1 Code                                            Explanation The <a href="http://stolenchair.     See previous. N...
THE BASICS what font to use if the preferred font is not available on the users computer. You can specify the margin and p...
CHAPTER 120
Chapter 2 Dice Game In this chapter, we will cover        •    drawing on canvas        •    random processing        •   ...
CHAPTER 2 Figure 2-1. First throw, resulting in a loss for the player It is not apparent here, but our dice game applicati...
DICE GAMEFigure 2-3. An 8 means a follow-up throw with a player s point of 8 carried over.Lets assume that the player even...
CHAPTER 2Critical requirements The requirements for building the dice game begin with simulating the random throwing of di...
DICE GAME You can use a similar approach to get whole numbers in any range. For example, if you want the numbers 1 to 13, ...
CHAPTER 2 userFirstThrow. You can see why it s called camel case—the capitals form “humps” in the word. You don t have to ...
DICE GAME the programmer chooses the name. Here s an example of a function definition that returns the product of the two ...
CHAPTER 2 and the second one as: Is the current value of the variable course the same as the string "Programming Games"? T...
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  1. 1. HTML5Using Games to Learn HTML5 and JavaScript
  2. 2. CONTENTSThe Essential Guide to HTML5 Using Games to Learn HTML5 and JavaScript Jeanine Meyer i
  3. 3. CONTENTS The Essential Guide to HTML5: Using Games to Learn HTML5 and JavaScript Copyright © 2010 by Jeanine Meyer All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system, without the prior written permission of the copyright owner and the publisher. ISBN-13 (pbk): 978-1-4302-3383-1 ISBN-13 (electronic): 978-1-4302-3384-8 Printed and bound in the United States of America (POD)Trademarked names, logos, and images may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, logos, or image we use the names, logos, or images only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark.The use in this publication of trade names, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Distributed to the book trade worldwide by Springer Science+Business Media LLC., 233 Spring Street, 6th Floor, New York, NY 10013. Phone 1-800-SPRINGER, fax (201) 348-4505, e-mail orders-ny@springer-sbm.com, or visit www.springeronline.com. For information on translations, please e-mail rights@apress.com or visit www.apress.com. Apress and friends of ED books may be purchased in bulk for academic, corporate, or promotional use. eBook versions andlicenses are also available for most titles. For more information, reference our Special Bulk Sales–eBook Licensing web page at www.apress.com/info/bulksales. The information in this book is distributed on an “as is” basis, without warranty. Although every precaution has been taken inthe preparation of this work, neither the author(s) nor Apress shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in this work. The source code for this book is freely available to readers at www.friendsofed.com in the Downloads section. Credits President and Publisher: Coordinating Editor: Paul Manning Debra Kelly Lead Editor: Copy Editor: Ben Renow-Clarke Sharon Terdeman Technical Reviewer: Compositor: Cheridan Kerr Bronkella Publishing Editorial Board: Indexer: Clay Andres, Steve Anglin, Mark Beckner, Brenda Miller Ewan Buckingham, Gary Cornell, Jonathan Gennick, Jonathan Hassell, Artist: Michelle Lowman, Matthew Moodie, April Milne Duncan Parkes, Jeffrey Pepper, Frank Pohlmann, Douglas Pundick, Cover Artist; Corné van Dooren Ben Renow-Clarke, Dominic Shakeshaft, Matt Wade, Tom Welsh Cover Designer: Anna Ishchenko
  4. 4. CONTENTSTo Daniel, Aviva, Anne, Esther, and Joseph, who is still in our lives, and for the newest members of the family: Allison, Liam, and Grant. iii
  5. 5. CONTENTS Contents at a Glance Contents at a Glance................................................................................................ iv Contents..................................................................................................................... v About the Author ...................................................................................................... x About the Technical Reviewer ............................................................................... xi Acknowledgments ................................................................................................... xii Introduction ............................................................................................................ xiii Chapter 1: The Basics ............................................................................................... 1 Chapter 2: Dice Game ............................................................................................. 21 Chapter 3: Bouncing Ball ........................................................................................ 67 Chapter 4: Cannonball and Slingshot ..................................................................... 97 Chapter 5: The Memory (aka Concentration) Game ............................................ 141 Chapter 6: Quiz...................................................................................................... 179 Chapter 7: Mazes ................................................................................................... 213 Chapter 8: Rock, Paper, Scissors ........................................................................ 259 Chapter 9: Hangman .............................................................................................. 287 Chapter 10: Blackjack............................................................................................ 317 Index ....................................................................................................................... 347iv
  6. 6. CONTENTSContentsContents at a Glance................................................................................................ ivContents..................................................................................................................... vAbout the Author ...................................................................................................... xAbout the Technical Reviewer ............................................................................... xiAcknowledgments ................................................................................................... xiiIntroduction ............................................................................................................ xiiiChapter 1: The Basics ............................................................................................... 1 Introduction .....................................................................................................................................................1 Critical requirements .......................................................................................................................................3 HTML5, CSS, and JavaScript features ..........................................................................................................4 Basic HTML structure and tags ..................................................................................................................4 JavaScript programming ...........................................................................................................................10 Building the application and making it your own ..........................................................................................11 Testing and uploading the application..........................................................................................................19 Summary ........................................................................................................................................................19Chapter 2: Dice Game ............................................................................................. 21 Introduction ...................................................................................................................................................21 Critical requirements .....................................................................................................................................24 HTML5, CSS, and JavaScript features ........................................................................................................24 Pseudo-random processing and mathematical expressions..................................................................24 Variables and assignment statements .....................................................................................................25 Programmer-defined functions .................................................................................................................26 Conditional statements: if and switch ......................................................................................................27 Drawing on the canvas ..............................................................................................................................29 Building the application and making it your own ..........................................................................................38 Throwing a single die .................................................................................................................................40 Throwing two dice ......................................................................................................................................47 The complete game of craps .....................................................................................................................55 v
  7. 7. CONTENTS Testing and uploading the application..........................................................................................................65 Summary ........................................................................................................................................................65 Chapter 3: Bouncing Ball ........................................................................................ 67 Introduction ...................................................................................................................................................67 Critical requirements .....................................................................................................................................70 HTML5, CSS, JavaScript features ...............................................................................................................70 Drawing a ball, image, and gradient ..........................................................................................................70 Building the application and making it your own ..........................................................................................80 Testing and uploading the application..........................................................................................................96 Summary ........................................................................................................................................................96 Chapter 4: Cannonball and Slingshot ..................................................................... 97 Introduction ...................................................................................................................................................97 Critical requirements ...................................................................................................................................100 HTML5, CSS, and JavaScript features ......................................................................................................101 Arrays and programmer-defined objects ................................................................................................101 Rotations and translations for drawing...................................................................................................103 Drawing line segments.............................................................................................................................107 Mouse events for pulling on the slingshot..............................................................................................108 Changing the list of items displayed using array splice ........................................................................110 Distance between points .........................................................................................................................110 Building the application and making it your own ........................................................................................111 Cannonball: with cannon, angle, and speed ..........................................................................................118 Slingshot: using a mouse to set parameters of flight ............................................................................128 Testing and uploading the application........................................................................................................140 Summary ......................................................................................................................................................140 Chapter 5: The Memory (aka Concentration) Game ............................................ 141 Introduction .................................................................................................................................................141 Critical requirements ...................................................................................................................................146 HTML5, CSS, JavaScript features .............................................................................................................146 Representing cards .................................................................................................................................146 Using Date for timing ...............................................................................................................................147 Providing a pause ....................................................................................................................................148vi
  8. 8. CONTENTS Drawing text .............................................................................................................................................149 Drawing polygons ....................................................................................................................................151 Shuffling cards.........................................................................................................................................152 Implementing clicking on a card..............................................................................................................152 Preventing certain types of cheating .....................................................................................................153 Building the application and making it your own ........................................................................................154 Testing and uploading the application........................................................................................................177 Summary ......................................................................................................................................................177Chapter 6: Quiz...................................................................................................... 179 Introduction .................................................................................................................................................179 Critical requirements ...................................................................................................................................183 HTML5, CSS, and JavaScript features ......................................................................................................184 Storing and retrieving information in arrays ...........................................................................................184 Creating HTML during program execution ..............................................................................................186 Changing elements by modifying CSS using JavaScript code .............................................................189 Text feedback using form and input elements .......................................................................................190 Presenting video......................................................................................................................................191 Building the application and making it your own ........................................................................................193 Testing and uploading the application........................................................................................................210 Summary ......................................................................................................................................................210Chapter 7: Mazes ................................................................................................... 213 Introduction .................................................................................................................................................213 Critical requirements ...................................................................................................................................218 HTML5, CSS, and JavaScript features ......................................................................................................219 Representation of walls and the token ...................................................................................................219 Mouse events to build and position a wall ..............................................................................................219 Detecting the arrow keys ........................................................................................................................220 Collision detection: token and any wall ..................................................................................................222 Using local storage ..................................................................................................................................224 Encoding data for local storage ..............................................................................................................230 Radio buttons...........................................................................................................................................231 vii
  9. 9. CONTENTS Building the application and making it your own ........................................................................................232 Creating the second maze application ...................................................................................................246 Testing and uploading application ..............................................................................................................257 Summary ......................................................................................................................................................257 Chapter 8: Rock, Paper, Scissors ........................................................................ 259 Introduction .................................................................................................................................................259 Critical requirements ...................................................................................................................................262 HTML5, CSS, and JavaScript features ......................................................................................................263 Providing graphical buttons for the player .............................................................................................263 Generating the computer move ..............................................................................................................267 Starting off ...............................................................................................................................................274 Building the application and making it your own ........................................................................................275 Testing and uploading the application........................................................................................................284 Summary ......................................................................................................................................................285 Chapter 9: Hangman .............................................................................................. 287 Introduction .................................................................................................................................................287 Critical requirements ...................................................................................................................................295 HTML5, CSS, JavaScript features .............................................................................................................295 Storing a word list as an array defined in an external script file ............................................................295 Generating and positioning HTML markup, then making the markup be buttons, and then disabling the buttons .....................................................................................................................................................296 Creating progressive drawings on a canvas ..........................................................................................298 Maintaining the game state and determining a win or loss ....................................................................300 Checking a guess and revealing letters in the secret word by setting textContent ............................301 Building the application and making it your own ........................................................................................302 Testing and uploading the application........................................................................................................315 Summary ......................................................................................................................................................315 Chapter 10: Blackjack............................................................................................ 317 Introduction .................................................................................................................................................317 Critical requirements ...................................................................................................................................322 HTML5, CSS, and JavaScript features ......................................................................................................323 Building the application and making it your own ........................................................................................330viii
  10. 10. CONTENTS Testing and uploading the application........................................................................................................346 Summary ......................................................................................................................................................346Index ....................................................................................................................... 347 ix
  11. 11. CONTENTS About the Author Jeanine Meyer is a Full Professor at Purchase College/State University of New York. She teaches courses for mathematics/computer science and new media majors, as well as a mathematics class for humanities students. The web site for her academic activities is http://faculty.purchase.edu/jeanine.meyer. Before coming to academia, she was a Research Staff Member and Manager at IBM Research, working on robotics and manufacturing research and later as a consultant for IBMs educational grant programs. For Jeanine, programming is both a hobby and a vocation. Every day she plays computer puzzles online (set game, kakuru, hashi, hitori and—often, still—tetris), and she does the crossword puzzle and ken ken in the newspaper (by hand and in ink—it s easier that way). She enjoys cooking, baking, eating, gardening, travel, and a moderate amount of walking. She greatly enjoys listening to her mother play piano and occasionally plays the flute. She is an active volunteer for progressive causes and candidates.x
  12. 12. CONTENTSAbout the Technical ReviewerCheridan Kerr has been involved in Web Development and Design since 1997 when she began working ina research team for the Y2K Millennium Bug. It was here she learned about the Internet and promptly fell inlove with the medium. In her career she has been responsible for web sites in the early 00s such as WeightWatchers Australia and Quicken.com.au, and she worked as Creative Services Manager of Yahoo!7 inAustralia on clients such as Toyota, 20th Century Fox, and Ford. Currently she is working as Head ofDigital for an Australian advertising agency. xi
  13. 13. CONTENTS Acknowledgments Much appreciation to my students and colleagues at Purchase College/State University of New York for their inspiration, stimulation, and support. Thanks to the crew at friends of ED: Ben Renow-Clarke, who encouraged me even before I quite grasped the idea of writing this book; Debra Kelly, who is an excellent project manager—which I needed; Cheridan Kerr, the technical reviewer, who provided important suggestions; and the art manager and many others I dont know by name. And lastly, thanks to you, the reader. I am confident you can build on these ideas to make wonderful web sites.xii
  14. 14. CONTENTSIntroductionThere s been considerable enthusiasm about the new capabilities of HTML5, and even suggestions thatno other technologies or products are necessary to produce dynamic, engrossing, interactive web sites.That may be overstating things, but it is true the new features are exciting. It now is possible, using justHTML5, Cascading Style Sheets, and JavaScript, to draw lines, arcs, circles and ovals on the screen andspecify events and event handling to produce animation and respond to user actions. You can includevideo and audio on your web site with standard controls, or place the video or audio in your applicationexactly when needed. You can create forms that validate the input and provide immediate feedback tousers. You can use a facility similar to cookies to store information on the client computer. And you canuse new elements, such as header and footer, to help structure your documents.This book is based on my teaching practices and past writings. Delving into the features of a technologyor general programming concepts is best done when there is a need. Games, especially familiar andsimple ones, supply the need and thus the motivation and much of the explanation. When learning a newprogramming language, my first step is to program the game of craps. If I can build a ballistics simulationwith animation, such as the slingshot game, and make a video or audio clip play when a specific conditionoccurs, I am happy. If I can construct my own maze of walls, draw a stick figure for hangman, and storeinformation on the players computer, I am ecstatic. And that s what we do in this book. As you see how tobuild these simple games, you ll build your expertise as well.This goal of this book, developed with considerable help from the friends of ED staff and the technicalreviewer, is to prepare you to produce your own web sites, including games and other dynamicapplications, with a gentle introduction to the essentials of HTML5 and programming.At the time of writing this book, not all browsers support all the HTML5 features. The applications havebeen tested using Chrome, FireFox, and Safari.Who is this book for?This book is for people who want to learn how HTML 5 can help build dynamic, exciting web sites. It s foryou if you know something about programming and want to see what HTML 5 brings to the table. And it salso for you if you have no programming experience whatsoever. Perhaps you re a web designer or website owner and you want to know how to make things happen behind the scenes. With this book, we wantto showcase the new features of HTML5 and demystify the art of programming. Programming is an art, andcreating appealing games and other applications requires real talent. However, if you can put togetherwords to form sentences and sentences to form paragraphs, and you have some sense of logic, you canprogram.How is this book structured?The book consists of 10 chapters, each organized around a familiar game or similar application. There isconsiderable redundancy among the chapters so you can skip around if you like, though the games do getmore complex. Each chapter starts by listing the technical features that will be covered and describing theapplication. We look first at the critical requirements in a general sense: what do we need to implement theapplication, independent of any specific technology. We then focus on the features of HTML5, CSS, xiii
  15. 15. INTRODUCTION CONTENTS JavaScript, or general programming methodology that satisfy the requirements. Finally, we examine the implementation of the application in detail. I break out the code line by line in a table, with comments next to each line. In the cases where multiple versions of a game are described, only the new lines of code are annotated. This isnt to deprive you of information, but encourage you to see what is similar, what is different, and how you can build applications in stages. Each chapter includes suggestions on how to make the application your own, and how to test and upload the application to a web site. The summary at the end of each chapter highlights what you ve learned and what you ll find ahead. Conventions used in this book The applications in this book each are HTML documents. The JavaScript is in a script element in the head element and the CSS is in the style element in the head element. The body element contains the static html, including any canvas elements. Several examples depend on external image files and one example requires external video files and another external audio files. Layout conventions To keep this book as clear and easy to follow as possible, the following text conventions are used throughout: • Important words or concepts are normally highlighted on the first appearance in italic type. • Code is presented in fixed-width font. • The complete code for each application is presented in table with the left hand column holding each statement and the right hand column holding an explanatory comment. • Pseudo-code is written in italic fixed-width font . • Sometimes code won t fit on a single line in a book. Where this happens, I use an arrow like this: ➥. So, with the formalities out of the way, let s get started.xiv
  16. 16. Chapter 1 The Basics In this chapter, we will cover • the basic structure of an HTML document • the html, head, title, script, style, body, img, and a elements • a Cascading Style Sheet (CSS) example • a JavaScript code example, using Date and document.writeIntroduction Hypertext Markup Language (HTML) is the language for delivering content on the Web. HTML is not owned by anyone, but is the result of people working in many countries and many organizations to define the features of the language. An HTML document is a text document which you can produce using any text editor. HTML documents contain elements surrounded by tags—text that starts with a < symbol and ends with a > symbol. An example of a tag is <img src="home.gif"/>. This particular tag will display the image held in the file home.gif. These tags are the markup. It is through the use of tags that hyperlinks, images, and other media are included in web pages. Basic HTML can include directives for formatting in a language called Cascading Style Sheets (CSS) and programs for interaction in a language called JavaScript. Browsers, such as Firefox and Chrome, interpret the HTML along with any CSS and JavaScript to produce what we experience when we visit a web site. HTML holds the content of the web site, with tags providing information on the nature and structure of the content as well as references to images and other media. CSS specifies the formatting. The same content can be formatted in different ways. JavaScript is a programming language that s used to make the web site dynamic and interactive. In all but the smallest working groups, different people may be responsible for the HTML, CSS, and JavaScript, but it s always a good idea to have a basic understanding of how these different tools work together. If you are already familiar with the basics of HTML and how CSS and JavaScript can be added together, you may want to skip ahead to the next chapter. Still, it may be worth casting your eye over the content in this chapter, to make sure you are up to speed on everything before we start on the first core examples. 1
  17. 17. CHAPTER 1 The latest version of HTML (and its associated CSS and JavaScript) is HTML5. It is generating considerable excitement because of features such as the canvas for displaying pictures and animation; support for video and audio; and new tags for defining common document elements such as header, section, and footer. You can create a sophisticated, highly interactive web site with the new HTML5. As of this writing, not all browsers accept all the features, but you can get started learning HTML5, CSS, and JavaScript now. Learning JavaScript will introduce you to general programming concepts that will be beneficial if you try to learn any other programming language or if you work with programmers as part of a team. The approach I ll use in this book is to explain HTML5, CSS, and JavaScript concepts in the context of specific examples, most of which will be familiar games. Along the way, I ll use small examples to demonstrate specific features. Hopefully, this will help you both understand what you want to do and appreciate how to do it. You will know where we are headed as I explain the concepts and details. The task for this chapter is to build a web page of links to other web sites. In this way, you ll get a basic understanding of the structure of an HTML document, with a small amount of CSS code and JavaScript code. For this and other examples, please think of how to make the project meaningful to you. The page could be a list of your own projects, favorite sites, or sites on a particular topic. For each site, you ll see text and a hyperlink. The second example includes some extra formatting in the form of boxes around the text, pictures, and the days date and time. Figure 1-1 and Figure 1-2 show the different examples I ve created. Figure 1-1. An annotated list of games2
  18. 18. THE BASICS Figure 1-2. Favorite sites, with extra formatting When you reload the Favorite Sites page, the date and time will change to the current date and time according to your computer.Critical requirements The requirements for the list of links application are the very fundamental requirements for building a web page containing text, links, and images. For the example shown in Figure 1-1, each entry appears as a paragraph. In the example shown in Figure 1-2, in contrast, each entry has a box around it. The second example also includes images and a way to obtain the current day, date, and time. Later applications will require more discussion, but for this one we ll go straight to how to implement it using HTML, CSS, and JavaScript. 3
  19. 19. CHAPTER 1HTML5, CSS, and JavaScript features As I noted, HTML documents are text, so how do we specify links, pictures, formatting, and coding? The answer is in the markup, that is, the tags. Along with the HTML that defines the content, you ll typically find CSS styles, which can be specified either inside the HTML document or in an external document. You might also include JavaScript for interactivity, again specified in the HTML document or in an external document. We ll start with a look at how you can build simple HTML tags, and how you can add inline CSS and JavaScript all within the same document.Basic HTML structure and tags An HTML element begins with a starting tag, which is followed by the element content and an ending tag. The ending tag includes a / symbol followed by the element type, for example /head. Elements can be nested within elements. A standard HTML document looks like this: <html> <head> <title>Very simple example </title> </head> <body> This will appear as is. </body> </html> Note that I ve indented the nested tags here to make them more obvious, but HTML itself ignores this indentation (or whitespace, as it s known), and you don t need to add it to your own files. In fact, for most of the examples throughout this book I won t be indenting my code. This document consists of the html element, indicated by the starting tag <html> and ending with the closing tag: </html>. HTML documents typically have a head and a body element, as this one has. This head element contains one element, title. The HTML title shows up different places in different browsers. Figure 1-3 shows the title, "Very Simple Example" at the top-left portion of the screen and also on a tab in Firefox. Figure 1-3. The HTML title in two places in Firefox4
  20. 20. THE BASICSIn most cases, you will create something within the body of the web page that you ll think of as a title, but itwon t be the HTML title! Figure 1-3 also shows the body of the web page: the short piece of text. Noticethat the words html, head, title and body do not appear. The tags “told” the browser how to display theHTML document.We can do much more with text, but lets go on to see how to get images to appear. This requires an imgelement. Unlike html, head, and body elements that use starting and ending tags, the img element justuses one tag. It is called a singleton tag. Its element type is img (not image) and you put all the informationwith the tag itself using what are termed attributes. What information? The most important item is the nameof the file that holds the image. The tag<img src="frog.jpg"/>tells the browser to look for a file with the name frog and the file type jpg. In this case, the browser looks inthe same directory or folder as the HTML file. You can also refer to image files in other places and I ll showthis later. The src stands for source. It is termed an attribute of the element. The slash before the >indicates that this is a singleton tag. There are common attributes for different element types, but mostelement types have additional attributes. Another attribute for img elements is the width attribute.<img src="frog.jpg" width="200"/>This specifies that the image should be displayed with a width of 200 pixels. The height will be whatever isnecessary to keep the image at its original aspect ratio. If you want specific widths and heights, even ifthat may distort the image, specify both width and height attributes.Tip: You ll see examples (maybe even some of mine) in which the slash is omitted and which workjust fine, but it is considered good practice to include it. Similarly, you ll see examples in which thereare no quotation marks around the name of the file. HTML is more forgiving in terms of syntax(punctuation) than most other programming systems. Finally, you ll see HTML documents that startwith a very fancy tag of type !DOCTYPE and have the HTML tag include other information. At thispoint, we dont need this so I will keep things as simple as I can (but no simpler, to quote Einstein).Producing hyperlinks is similar to producing images. The type of element for a hyperlink is a and theimportant attribute is href.<a href="http://faculty.purchase.edu/jeanine.meyer">Jeanine Meyers AcademicActivities </a>As you can see, this element has a starting and ending tag. The content of the element, whatever isbetween the two tags—in this case, Jeanine Meyers Academic Activities—is what shows up in blue andunderlined. The starting tag begins with a. One way to remember this is to think of it as the most importantelement in HTML, so it uses the first letter of the alphabet. You can also think of an anchor, which is whatthe a actually stands for, but that isnt as meaningful for me. The href attribute (think hypertextreference) specifies the web site where the browser goes when the hyperlink is clicked. Notice that this isa full Web address (called a Universal Resource Locator, or URL, for short).We can combine a hyperlink element with an img element to produce a picture on the screen that a usercan click on. Remember that elements can be nested within other elements. Instead of putting text afterthe starting <a> tag, put an <img> tag: 5
  21. 21. CHAPTER 1 <a href="http://faculty.purchase.edu/jeanine"> <img src="jhome.gif" width="100" /> </a> Let s put these examples together now: <html> <head> <title>Second example </title> </head> <body> This will appear as is. <img src="frog.jpg"/> <img src="frog.jpg" width="200"/> <a href=http://faculty.purchase.edu/jeanine.meyer>Jeanine Meyers Academic Activities </a> <a href=http://faculty.purchase.edu/jeanine.meyer><img src="jhome.gif"/></a> </body> </html> I created the HTML file, saved it as second.html, and then opened it up in the Chrome browser. Figure 1-4 shows what is displayed. Figure 1-4. Example with images and hyperlinks This produces the text; the image in its original width and height; the image with the width fixed at 200 pixels and height proportional; a hyperlink that will take you to my web page (I promise); and another link that uses an image that will also take you to my web page. However, this isnt quite what I had in mind. I wanted these elements spaced down the page. This demonstrates something you need to remember: HTML ignores line breaks and other white space. If you want a line break, you have to specify it. One way is to use the br singleton tag. I ll show other ways later. Take a look at the following modified code. Notice that the <br/> tags don t need to be on a line by themselves.6
  22. 22. THE BASICS<head><title>Second example </title><body>This will appear as is. <br/><img src="frog.jpg"/><br/><img src="frog.jpg" width="200"/><br/><a href=http://faculty.purchase.edu/jeanine.meyer>Jeanine Meyers Academic Activities </a><br/><a href=http://faculty.purchase.edu/jeanine.meyer><img src="jhome.gif"/></a></body></html>Figure 1-5 shows what this code produces.Figure 1-5. Text, images, and links with line breaksThere are many HTML element types: the h1 through h6 heading elements produce text of different sizes;there are various elements for lists and tables, and others for forms. CSS, as we ll see in a moment, is alsoused for formatting. You can select different fonts, background colors, and colors for the text, and controlthe layout of the document. It s considered good practice to put formatting in CSS, interactivity inJavaScript, and keep the HTML for the content. HTML5 provides new structural elements, such asarticle, section, footer, and header, and this makes it even easier to put the formatting in CSS. Doing 7
  23. 23. CHAPTER 1 this lets you easily change the formatting and the interactions. Formatting, including document layout, is a large topic. In this book, I stick to the basics.Using cascading style sheets CSS is a special language just for formatting. A style is essentially a rule that specifies how a particular element will be formatted. This means you can put style information in a variety of places: a separate file, a style element located in the head element, or a style within the HTML document, perhaps within the one element you want to format in a particular way. The styling information cascades, trickles down, unless a different style is specified. To put it another way, the style closest to the element is the one that s used. For example, you might use your official company fonts as given in the style section in the head element to flow through most of the text, but include specification within the local element to style one particular piece of text. Because that style is closest to the element, it is the one that is used. The basic format includes an indicator of what is to be formatted followed by one or more directives. In the application for this chapter (available at www.friendsofed.com/downloads.html), I ll specify the formatting for elements of type section, namely a border or box around each item, margins, padding, and alignment, and a background of white. The complete HTML document in Listing 1-1 is a mixture (some would say a mess!) of features. The elements body and p (paragraph) are part of the original version of HTML. The section element is one of the new element types added in HTML5. The section element does need formatting, unlike body and p, which have default formatting that the body and each p element will start on a new line. CSS can modify the formatting of old and new element types. Notice that the background color for the text in the section is different from the background color for the text outside the section. In the code in Listing 1-1, I specify styles for the body element (there is just one) and the section element If I had more than one section element, the styling would apply to each of them. The style for the body specifies a background color and a color for the text. CSS accepts a set of 16 colors by name, including black, white, red, blue, green, cyan, and pink. You can also specify color using RGB (red green blue) hexadecimal codes, but you ll need to use a graphics program, such as Adobe Photoshop, Corel Paint Shop Pro, or Adobe Flash Professional to figure out the RGB values, or you can experiment. I used Paint Shop Pro to determine the RGB values for the green in the frog head picture and used that for the border as well. The text-align directives are just what they sound like: they indicate whether to center the material or align it to the left. The font-size sets the size of text in pixels. Borders are tricky and don t appear to be consistent across browsers. Here I ve specified a solid green border of 4 pixels. The width specification for section indicates that the browser should use 85 percent of the window, whatever that is. The specification for p sets the width of the paragraph at 250 pixels. Padding refers to the spacing between the text and the borders of the section. The margin is the spacing between the section and its surroundings. Listing 1-1. A Complete HTML Document with Styles <html> <head> <title>CSS example </title> <style> body { background-color:tan;8
  24. 24. THE BASICS color: #EE015; text-align:center; font-size:22px;}section { width:85%; border:4px #00FF63 solid; text-align:left; padding:5px; margin:10px; background-color: white;}p { width: 250px;}</style></head><body>The background here is tan and the text is the totally arbitrary RED GREEN BLUE value #EE015. <br/><section>Within the section, the background color is white. There is text with additional HTML markup, followed by a paragraph with text. Then, outside the section there will be text, followed by an image, more text and then a hyperlink. <p>The border color of the section matches the color of the frog image. </p></section><br/>As you may have noticed, I like origami. The next image represents a frog head.<br/><img src="frogface.gif"/> <br/>If you want to learn how to fold it, go to<a href=http://faculty.purchase.edu/jeanine.meyer/origami>the Meyer Family Origami Page <img src="crane.png" width="100"/></a></body></html>This produces the screen shown in Figure 1-6. 9
  25. 25. CHAPTER 1 Figure 1-6. Sample CSS styles Tip: Don t be concerned if you don t understand everything immediately—you ll find lots of help on the Web. In particular, see the official source for HTML 5 at http://dev.w3.org/html5/ spec/Overview.html . There are many things you can do with CSS. You can use it to specify formatting for types of elements, as shown above; you can specify that elements are part of a class; and you can identify individual elements using the id attribute. In Chapter 6 where we create a quiz, I use CSS to position specific elements in the window and then JavaScript to move them around.JavaScript programming JavaScript is a programming language with built-in features for accessing parts of an HTML document, including styles in the CSS element. It is termed a scripting language to distinguish it from compiled languages, such as C++. Compiled languages are translated all at once, prior to use, while scripting languages are interpreted line by line by browsers. This text assumes no prior programming experience or knowledge of JavaScript, but it may help to consult other books, such as Getting Started with JavaScript, by Terry McNavage (friends of ED, 2010), or online sources such as http://en.wikipedia.org/wiki/JavaScript. Each browser owns its version of JavaScript. An HTML document holds JavaScript in a script element, located in the head element. To display the time and date information as shown in Figure 1-2, I put the following within the head element of the HTML document: <script> document.write(Date()); </script> JavaScript, like other programming languages, is made up of statements of various types. In later chapters, I ll show you assignment statements, compound statements such as if and switch and for10
  26. 26. THE BASICS statements, and statements that create what are called programmer-defined functions. A function is one or more statements that work together in a block and can be called anytime you need that functionality. Functions save writing out the same code over and over. JavaScript supplies many built-in functions. Certain functions are associated with objects (more on this later) and are called methods. The code document.write("hello"); is a JavaScript statement that invokes the write method of the document object with the argument "hello". An argument is additional information passed to a function or method. Statements are terminated by semicolons. This piece of code will write out the literal string of characters h, e, l, l, o as part of the HTML document. The document.write method writes out anything within the parentheses. Since I wanted the information written out to change as the date and time change, I needed a way to access the current date and time, so I used the built-in JavaScript Date function. This function produces an object with the date and time. Later, you ll see how to use Date objects to compute how long it takes for a player to complete a game. For now, all I want to do is display the current date and time information, and that s just what the code document.write(Date()); does. To use the formal language of programming: this code calls (invokes) the write method of the document object, a built-in piece of code. The period (.) indicates that the write to be invoked is a method associated with the document produced by the HTML file. So, something is written out as part of the HTML document. What is written out? Whatever is between the opening parenthesis and the closing parenthesis. And what is that? It is the result of the call to the built-in function Date. The Date function gets information maintained by the local computer and hands it off to the write method. Date also requires the use of parentheses, which is why you see so many. The write method displays the date and time information as part of the HTML document, as shown in Figure 1-2. The way these constructs are combined is typical of programming languages. The statement ends with a semi-colon. Why not a period? A period has other uses in JavaScript, such as indicating methods and also for decimal points for numbers. Natural languages, such as English, and programming languages have much in common: different types of statements; punctuation using certain symbols; and a grammar for the correct positioning of elements. In programming, we use the term notation instead of punctuation, and syntax instead of grammar. Both programming languages and natural languages also let you build up quite complex statements out of separate parts. However, there is a fundamental difference: As I tell my students, chances are good that much of what I say in class is not grammatically correct, but they ll still understand me. But when you re “talking” to a computer via a programming language, your code must be perfect in terms of the grammatical rules of the language to get what you want. The good news is that unlike a human audience, computers do not exhibit impatience or any other human emotion so you can take the time you need to get things right. There s also some bad news that may take you a while to appreciate: If you make a mistake in grammar— termed a syntactic error—in HTML, CSS, or JavaScript, the browser still tries to display something. It s up to you figure out what and where the problem is when you dont get the results you wanted in your work.Building the application and making it your own You build an HTML document using a text editor and you view/test/play the document using a browser. Though you can use any text editor program to write the HTML, I suggest TextPad for PCs and TextWrangler for Macs. These are shareware, which makes them relatively inexpensive. Don t use a word 11
  27. 27. CHAPTER 1 processing program, which may insert non-text characters. Notepad also works, though TextPad has benefits such as color-coding that I ll demonstrate. To use the editor, you open it up and type in the code. Figure 1-7 shows what the TextPad screen looks like. Figure 1-7. Starting off in TextPad You will want to save your work frequently and, most important, save it as the file type .html. In TextPad, click on File ➤ Save As and then change the Save as type to HTML, as shown in Figure 1-8. Figure 1-8. Saving a file as type HTML12
  28. 28. THE BASICSNotice that I gave the file a name and that I can also change the folder from My Documents to somethingelse if I want. After saving the file, and clicking on Configure ➤ Word Wrap (to make the long lines visibleon the screen), the window appears as shown in Figure 1-9.Figure 1-9. After saving the file as HTML and invoking word wrapThe color coding, which you ll see only after the file is saved as HTML, indicates tags and quoted strings.This can be valuable for catching many errors.Now let s delve into the HTML coding, first for the list of annotated links and then for the favorite sites. Thecode uses the features described in the previous section. Table 1-1 shows the complete code for thisapplication: paragraphs of text with links to different files, all located in the same folder. 13
  29. 29. CHAPTER 1 Table 1-1. The “My games” Annotated Links Code Code Explanation <html> Opening html tag <head> Opening head tag <title>Annotated links</title> Opening title tag, the title text and closing title tag <body> Opening body tag <h1>My games</h1> Opening h1 tag, text and then closing h1 tag. This will make “My games” appear in a big font. The actual font will be the default. <p> Opening p for paragraph tag The <a href="craps.html">Dice game</a> presents Text with an a element. The opening a tag the game called craps. has the attribute href set to the value craps.html. Presumably this is a file in the same folder as this HTML file. The contents of the a element—whatever is between the <a> and the </a>—will be displayed, first in blue and then in mauve once clicked, and underlined. </p> Closing p tag <p> Opening p tag The <a href="cannonball.html">Cannonball</a> is See the previous case. The a element here a ballistics simulation. A ball appears to move refers to the cannonball.html file and the on the screen in an arc. The program determines displayed text is Cannonball. when the ball hits the ground or the target. The player can adjust the speed and the angle. </p> Closing p tag <p> Opening p tag14
  30. 30. THE BASICSCode ExplanationThe <a href="slingshot.html">Slingshot</a> See previous. This paragraph contains thesimulates shooting a slingshot. A ball moves on hyperlink to slingshot.html.the screen, with the angle and speed dependingon how far the player has pulled back on theslingshot using the mouse.</p> Closing p tag<p> Opening p tagThe <a href="memory.html">Concentration/memory See previous. This paragraph contains thegame</a> presents a set of plain rectangles you hyperlink to memory.html.can think of as the backs of cards. The playerclicks on first one and then another andpictures are revealed. If the two picturesrepresent a match, the two cards are removed.Otherwise, the backs are displayed. The gamecontinues until all matches are made. The timeelapsed is calculated and displayed.</p> Closing p tag<p> Opening p tagThe <a href="quiz1.html">Quiz game</a> presents See previous. This paragraph contains thethe player with 4 boxes holding names of hyperlink to quiz1.htmlcountries and 4 boxes holding names of capitalcities. These are selected randomly from alarger list. The player clicks to indicatematches and the boxes are moved to put theguessed boxes together. The program displayswhether or not the player is correct.</p> Closing p tag<p> Opening p tag 15
  31. 31. CHAPTER 1 Code Explanation The <a href="maze.html">Maze</a> program is a See previous. This paragraph contains the multi-stage game. The player builds a maze by hyperlink to maze.html. using the mouse to build walls. The player then can move a token through the maze. The player can also save the maze on the local computer using a name chosen by the player and retrieve it later, even after closing the browser or turning off the computer. </p> Closing p tag </body> Closing body tag </html> Closing html tag The Favorite Site code has the features of the annotated list with the addition of formatting: a green box around each item and a picture in each item. See Table 1-2. Table 1-2. The Favorites Sites Code Code Explanation <html> Opening html tag <head> Opening head tag <title>Annotated links</title> Complete title element: opening and closing tag and Annotated links in between <style> Opening style tag. This means we re now going to use CSS. Article { Start of a style. The reference to what is being styled is all section elements. The style then has a brace - {. The opening and closing braces surround the style rule we re creating, much like opening and closing tags in HTML. width:60%; The width is set to 60% of the containing element. Note that each directive ends with a ; . text-align:left; Text is aligned to the left margin:10px; The margin is 10 pixels16
  32. 32. THE BASICSCode Explanation border:2px green double; The border is a 2-pIxel green double line padding:2px; The space between the text and the border is 2 pixels display:block; The article is a block, meaning there are line breaks before and after} Closes the style for article</style> Closing style tag<script> Opening script tag. We are now writing JavaScript codedocument.write(Date()); One statement of code: write out what is produced by the Date() call</script> Closing script tag<body> Opening body tag<h3>Favorite Sites</h3> Text surrounded by h3 and /h3 tags. This make the text appear somewhat larger than the norm.<article> Opening article tagThe <a href="../index.html">Jeanine This text will be subject to the style specified. It includesMeyers Academic Activities</a> an a element. Notice that the value for the href attribute isdisplays information on my current a relative reference: it says: go to the parent folder of theand past courses, along with current folder and then to the index.html file. Two periodspublications and other activities. (..) is computer-speak for “go back a folder level”, so if we were in the tree/fruit/apple folder, then ../index.html would take us back to the fruit folder to find the index file, and ../../index.html would take us back to the tree folder.</article> Closing article tag<article> Opening article tag 17
  33. 33. CHAPTER 1 Code Explanation The <a href="http://stolenchair. See previous. Notice that the value for the href attribute org">Stolen Chair Theatre here is a full Web address, and that the HTML includes a Company</a> is the web site of a <br/> tag. This will force a line break. theatre company performing mainly in New York City. This is the postcard for their Summer, 2010 production.<br/> <img src="postcard.jpg" An img tag. The source of the image is the file width="300"/> postcard.jpg. The width is set at 300 pixels. </article> Closing article tag <article> Opening article tag The <a href="http://friendsofed See previous. This also refers to a Web address. A <br/> .com/">friends of ED publishers</a> tag will force a line break before the image. is the site for the publishers of this book. <br/> <img src="friendsofed.gif" An img element. The source is friendsofed.gif. The width is width="300"/> set at 300 pixels. </article> Closing article tag </body> Closing body tag </html> Closing html tag It is pretty straightforward how to make this application your own: use your own favorite sites. In most browsers, you can download and save image files if you want to use a site logo for the hyperlink, or you can include other pictures. It is my understanding that making a list of sites with comments and including images such as logos is within the practice called “fair use,” but I am not a lawyer. For the most part, people like links to their sites. It doesn t affect the legal question, but you can also choose to set the src in the img tag to the Web address of the site where the image lives if you d rather not download a particular image file to your computer and then upload it to your web site. Web addresses can be absolute or relative. An absolute address starts with http://. A relative address is relative to the location of the HTML file. In my example, the postcard.jpg and the friendsofed.gif are both located in the same folder as my HTML file. They are there because I put them there! For large projects, many people put all the images in a subfolder called images and write addresses as "images/postcard.gif". You also can make this application your own by changing the formatting. Styles can be used to specify fonts, including specific font, font family, and size. This lets you pick a favorite font, and also specify18
  34. 34. THE BASICS what font to use if the preferred font is not available on the users computer. You can specify the margin and padding or vary independently the margin-top, margin-left, padding-top, and so forth.Testing and uploading the application You need to have all the files, in this case the single HTML file plus all image files, in the same folder unless you are using full Web addresses. For the links to work, you need to have the correct addresses for all href attributes. My examples show how to do this for HTML files in the same folder or for HTML files somewhere else on the Web. You can start testing your work even if it is not completely done. For example, you can put in a single img element or a single a element. Open up a browser, such as Firefox, Chrome, or Safari (I didn t mention Internet Explorer because it does not yet support some of the HTML5 features I ll be using in other tutorials, though support is coming in IE9). In Firefox, click on File and then Open file and browse to your HTML file. In Chrome, press Ctrl on the PC (CMD on the MAC) and o and then browse to the file and click OK to open it. You should see something like my examples. Click on the hyperlinks to get to the other sites. Reload the page using the reload icon for the browser and observe the different time. If you dont see what you expect—something like my examples—you need to examine your code. Common mistakes are • missing or mismatched opening and closing tags. • wrong name for image files or HTML files, or wrong file extension for the image files. You can use image files of type JPG, GIF, or PNG but the file extension named in the tag must match the actual file type of the image. • missing quotation marks. The color coding, as available in TextPad and some other editors, can help you identify this.Summary In this chapter, you learned how to compose HTML documents with text, images, and hyperlinks. This included • the basic tags, including html, head, title, style, script, body. • the img element for displaying images. • the a element for hyperlinks. • simple formatting using a style element written following Cascading Style Sheet (CSS) rules. • a single line of JavaScript code to provide date and time information. This chapter was just the beginning, though it s possible to produce beautiful and informative web pages using basic HTML, with or without Cascading Style Sheets. In the next chapter, you will learn how to include randomness and interactivity in an application, and how to use the canvas element, the critical feature of HTML5. 19
  35. 35. CHAPTER 120
  36. 36. Chapter 2 Dice Game In this chapter, we will cover • drawing on canvas • random processing • game logic • form outputIntroduction Among the most important new features in HTML5 is the canvas. This element provides a way for developers to make line drawings, include images, and position text in a totally free-form fashion, a significant improvement over the older HTML. Although you could do some fancy formatting in the earlier versions, layouts tended to be boxy and pages less dynamic. How do you draw on the canvas? You use a scripting language, usually JavaScript. I will show you how to draw on canvas and I ll explain the important features of JavaScript that we ll need to build an implementation of the dice game called craps: how to define a function, how to invoke what is termed pseudo-random behavior, how to implement the logic of this particular game, and how to display information to a player. Before we go any further, though, you need to understand the basics of the game. The game of craps has the following rules: The player throws a pair of dice. The sum of the two top faces is what matters so a 1 and a 3 is the same as 2 and 2. The sum of two 6-sided dice can be any number from 2 to 12. If the player throws a 7 or 11 on the first throw, the player wins. If the player throws a 2, 3, or 12, the player loses. For any other result (4, 5, 6, 8, 9, 10), this result is recorded as what is called the players point and a follow-up throw is required. On follow-up throws, a throw of 7 loses and a throw of the players point wins. For anything else, the game continues with the follow-up throw rules. Let s see what our game play might look like. Figure 2-1 shows the result of a throw of two ones at the start of the game. 21
  37. 37. CHAPTER 2 Figure 2-1. First throw, resulting in a loss for the player It is not apparent here, but our dice game application draws the die faces each time using the canvas tag. This means it s not necessary to download images of individual die faces. A throw of two 1s means a loss for the player since the rules define 2, 3, or 12 on a first throw as a loss. The next example shows a win for the player, a 7 on a first throw, as shown in Figure 2-2. Figure 2-2. A 7 on a first throw means the player wins. Figure 2-3 shows the next throw—an 8. This is neither a win nor a loss, but means there must be a follow- up throw.22
  38. 38. DICE GAMEFigure 2-3. An 8 means a follow-up throw with a player s point of 8 carried over.Lets assume that the player eventually throws an 8 again, as indicated in Figure 2-4.Figure 2-4. It s another throw of 8, the point value, so the player wins.As the previous sequence shows, the only thing that counts is the sum of the values on the faces of thedice. The point value was set with two 4s, but the game was won with a 2 and a 6.The rules indicate that a game will not always take the same number of throws of the dice. The player canwin or lose on the first throw, or there may be any number of follow-up throws. It is the game builders job isto build a game that works—and working means following the rules, even if that means play goes on andon. My students sometimes act as if their games only work if they win. In a correct implementation of thegame, players will win and lose. 23
  39. 39. CHAPTER 2Critical requirements The requirements for building the dice game begin with simulating the random throwing of dice. At first, this seems impossible since programming means specifying exactly what the computer will do. Luckily, JavaScript, like most other programming languages, has a built-in facility that produces results that appear to be random. Sometimes languages make use of the middle bits (1s and 0s) of a very long string of bits representing the time in milliseconds. The exact method isn t important to us. We will assume that the JavaScript furnished by the browser does an okay job with this, which is called pseudo-random processing. Assuming now that we can randomly get any number from 1 to 6 and do it twice for the two die faces, we need to implement the rules of the game. This means we need a way to keep track of whether we are at a first throw or a follow-up throw. The formal name for this is the application state, which means the way things are right now, and is important in both games and other types of applications. Then we need to use constructs that make decisions based on conditions. Conditional constructs such as if and switch are a standard part of programming languages, and you ll soon understand why computer science teachers like me—who have never been in a casino or a back alley—really like the game of craps. We need to give the player a way to throw the dice, so we ll implement a button on the screen to click for that. Then we need to provide information back to the player on what happened. For this application, I produced graphical feedback by drawing dice faces on the screen and also displayed information as text to indicate the stage of the game, the point value, and the result. The older term for interactions with users was input-output (I/O), back when that interaction mainly involved text. The term graphical user interface (GUI) is now commonly used to indicate the vast variety of ways that users interact with computer systems. These include using the mouse to click on a specific point on the screen or combining clicks with dragging to simulate the effect of moving an object (see the slingshot game in Chapter 4). Drawing on the screen requires the use of a coordinate system to specify points. Coordinate systems for the computer screen are implemented in similar ways in most programming languages, as I ll explain shortly.HTML5, CSS, and JavaScript features Let s now take a look at the specific features of HTML5, CSS, and JavaScript that provide what we need to implement the craps game.Pseudo-random processing and mathematical expressions Pseudo-random processing in JavaScript is performed using a built-in method called Math.random. Formally, random is a method of the Math class. The Math.random method generates a number from 0 up to, but not including 1, resulting in a decimal number, for example, 0.253012. This may not seem immediately useful for us, but it s actually a very simple process to convert that number into one we can use. We multiply that number, whatever it is, by 6, which produces a number from 0 up to but not including 6. For example, if we multiply the .253012 by 6 we get 1.518072. That s almost what we need, but not quite. The next step is to strip away the fraction and keep the whole number. To do that, we make use of another Math method, Math.floor. This method produces a whole number after removing any fractional part. As the name suggests, the floor method rounds down. In our particular case, we started with .253012, then arrived at 1.518072, so the result is the whole number 1. In general, when we multiply our random number by 6 and floor it, we ll get a number from 0 to 5. The final step is to add a 1, because our goal is to get a number from 1 to 6, over and over again, with no particular pattern.24
  40. 40. DICE GAME You can use a similar approach to get whole numbers in any range. For example, if you want the numbers 1 to 13, you d multiply the random number by 13 and then add 1. This could be useful for a card game. You ll see similar examples throughout this book. We can combine all of these steps together into what is called an expression. Expressions are combinations of constants, methods, and function calls, and some things we ll explore later. We put these items together using operators, such as + for addition and * for multiplication. Remember from Chapter 1 how tags can be combined—nesting a tag within another tag—and the one line of JavaScript code we used in the Favorite Sites application: document.write(Date()); We can use a similar process here. Instead of having to write the random call and then the floor method as separate statements, we can pass the random call as an argument of the floor method. Take a look at this code fragment: 1+Math.floor(Math.random()*6) This expression will produce a number from 1 to 6. I call it a code fragment because it isnt quite a statement. The operators + and * refer to the arithmetic operations and are the same as you d use in normal math. The order of operations starts from the inside and works out. • Invoke Math.random() to get a decimal number from 0 up to, but not quite 1. • Multiply the result by 6. • Take that and strip away the fraction, leaving the whole number, using Math.floor. • Add 1. You ll see a statement with this expression in our final code, but we need to cover a few other things first.Variables and assignment statements Like other programming languages, JavaScript has a construct called a variable, which is essentially a place to put a value, such as a number. It is a way of associating a name with a value. You can use the value later by referencing the name. One analogy is to office holders. In the USA, we speak of “the president.” Now, in 2010, the president is Barack Obama. Before January 21, 2009, it was George W. Bush. The value held by the term “the president” changes. In programming, the value of the variable can vary as well, hence the name. The term var is used to declare a variable. The names of variables and functions, described in the next section, are up to the programmer. There are rules: no internal blanks and the name must start with an alphabetic character. Dont make the names too long as you dont want to type too much, but dont make them so short you forget what they are. You do need to be consistent, but you dont need to obey the rules of English spelling. For example, if you want to set up a variable to hold the sum of values and you believe that sum is spelled som, that s fine. Just make sure you use som all the time. But if you want to refer to something that s a part of JavaScript, such as function or document or random, you need to use the spelling that JavaScript expects. You should avoid using the names of built-in constructs in JavaScript (such as random or floor) for your variables. Try to make the names unique, but still easily understandable. One common method of writing variable names is to use what s called camel case. This involves starting your variable name in lower case, then using a capital letter to denote when a new word starts, for example, numberOfTurns or 25
  41. 41. CHAPTER 2 userFirstThrow. You can see why it s called camel case—the capitals form “humps” in the word. You don t have to use this naming method, but it s a convention many programmers follow. The line of code that will hold the pseudo-random expression explained in the previous section is a particular type of statement called an assignment statement. For example, var ch = 1+Math.floor(Math.random()*); sets the variable named ch to the value that is the result of the expression on the right-hand side of the equal sign. When used in a var statement, it also would be termed an initialization statement. The = symbol is used for setting initial values for variables as in this situation and in the assignment statements to be described next. I chose to use the name ch as shorthand for choice. This is meaningful for me. In general, though, if you need to choose between a short name and a longer one that you will remember, pick the longer one! Notice that the statement ends with a semi-colon. You may ask, why not a period? The answer is that a period is used in two other situations: as a decimal point and for accessing methods and properties of objects, as in document.write. Assignment statements are the most common type of statements in programming. Here s an example of an assignment statement for a variable already defined: bookname = "The Essential Guide to HTML5"; The use of the equal sign may be confusing. Think of it as making it true that the left-hand side equals what s produced by the right-hand side. You ll encounter many other variables and other uses of operators and assignment statements in this book. Caution: The var statement defining a variable is called a declaration statement. JavaScript, unlike many other languages, allows programmers to omit declaration statements and just start to use a variable. I try to avoid doing that, but you will see it in many online examples. For the game of craps, we need variables that define the state of the game, namely whether it is a first throw or a follow-up throw, and what the players point is (remember that the point is the value of the previous throw). In our implementation, these values will be held by so-called global variables, variables defined with var statements outside of any function definition so as to retain their value (the values of variables declared inside of functions disappear when the function stops executing). You don t always need to use variables. For example, the first application we create here sets up variables to hold the horizontal and vertical position of the dice. I could have put literal numbers in the code because I dont change these numbers, but since I refer to these values in several different places, storing the values in variables mean that if I want to change one or both, I only need to make the change in one place.Programmer-defined functions JavaScript has many built-in functions and methods, but it doesn t have everything you might need. For example, as far as I know, it does not have functions specifically for simulating the throwing of dice. So JavaScript lets us define and use our own functions. These functions can take arguments, like the Math.floor method, or not, like Math.random. Arguments are values that may be passed to the function. Think of them as extra information. The format for a function definition is the term function followed by the name you want to give the function, followed by parentheses holding the names of any arguments, followed by an open bracket, some code, and then a closed bracket. As I note in the previous sections,26
  42. 42. DICE GAME the programmer chooses the name. Here s an example of a function definition that returns the product of the two arguments. As the name indicates, you could use it to compute the area of a rectangle. function areaOfRectangle(wd,ln) { return wd * ln; } Notice the return keyword. This tells JavaScript to send the result of the function back to us. In our example, this lets us write something like rect1 = areaOfRectangle(5,10), which would assign a value of 50 (5 10) to our rect1 variable. The function definition would be written as code within the script element. It might or might not make sense to define this function in real life because it is pretty easy to write multiplication in the code, but it does serve as a useful example of a programmer-defined function. Once this definition is executed, which probably would be when the HTML file is loaded, other code can use the function just by calling its name, as in areaOfRectangle(100,200) or areaOfRectangle(x2- x1,y2-y1). The second expression assumes that x1, x2, y1, y2 refer to coordinate values that are defined elsewhere. Functions also can be called by setting certain tag attributes. For example, the body tag can include a setting for the onLoad attribute: <body onLoad="init();"> My JavaScript code contains the definition of a function I call init. Putting this into the body element means that JavaScript will invoke my init function when the browser first loads the HTML document or whenever the player clicks on the reload/refresh button. Similarly, making use of one of the new features of HTML5, I could include the button element: <button onClick="throwdice();">Throw dice </button> This creates a button holding the text Throw dice. When the player clicks it, JavaScript invokes the throwdice function I defined in the script element. The form element, to be described later, could invoke a function in a similar way.Conditional statements: if and switch The craps game has a set of rules. One way to summarize the rules is to say, if it is a first-throw situation, we check for certain values of the dice throw. If it s not the first throw, we check for other values of the dice throw. JavaScript provides the if and switch statements for such purposes. The if statement is based on conditions, which can be a comparison or a check for equality—for example, is a variable named temp greater than 85 or does the variable named course hold the value "Programming Games". Comparisons produce two possible logical values—true or false. So far you ve seen values that are numbers and values that are strings of characters. Logical values are yet another data type. They are also called Boolean values, after the mathematician, George Boole. The condition and check that I mentioned would be written in code as temp>85 and course == "Programming Games" Read the first expression as: Is the current value of the variable temp greater than 85? 27
  43. 43. CHAPTER 2 and the second one as: Is the current value of the variable course the same as the string "Programming Games"? The comparison example is easy to understand; we use > to check if one value is greater than another, and < to check the opposite. The value of the expression will be one of the two logical values true or false. The second expression is probably a little more confusing. You may be wondering about the two equal signs and maybe also the quotation marks .The comparison operator in JavaScript (and several other programming languages) that checks for equality is this combination of two equal signs. We need two equal signs because the single equal sign is used in assignment statements and it cant do double duty. If we had written course = "Programming Games", we would have been assigning the value "Programming Games" to our course variable rather than comparing the two items. The quotation marks define a string of characters, starting with P, including the space, and ending with s. With that under our belts, we can now take a look at how to write code that does something only if a condition is true. if (condition) { code } If we want our code to do one thing if a condition is true and another thing if it is NOT true, the format is: if (condition) { if true code } else { if not true code } Note that I used italics here because this is what is called pseudo-code, not real JavaScript that we would include in our HTML document. Here are some real code examples. They make use of alert, a built-in function that causes a small window with the message indicated by the argument given between the parentheses to pop up in the browser. The user must click OK to continue. if (temp>85) { alert("It is hot!"); } if (age > 21) { alert("You are old enough to buy a drink."); } else { alert("You are too young to be served in a bar."); } We could write the craps application using just if statements. However, JavaScript supplies another construct that makes things easier—the switch statement. The general format is: switch(x) { case a:28

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